<!DOCTYPE html>
<html lang="en">
<head>
    <meta http-equiv="content-type" content="text/html;charset=UTF-8">
    <title>Title</title>
    <style>
        .item{
            background-color: #dddddd;
        }
        .item:hover{
            color: red; /*当鼠标移动到item上时，字体颜色变为红色*/
        }
        .item:hover .c2{
            background-color: green;  /* 不论鼠标从上还是从下，移动到item时，c2的背景颜色变为绿色 */
        }
    </style>
</head>
<body>

<div class="item">
    <div class="c1">123</div>
    <div class="c2">456</div>
</div>


</body>
</html>